I currently only have Warlords. Does BTS enhance game play? and to be really competitive should i play BTS? or just stick with warlords?

BTS does enhance the gameplay a lot - imho. As for beeing competetive - it depends on who you want to compete to :p

GET BTS!!

I can't imagine playing Civ without it.

You won't regret it.

It adds a lot of depth to the game. Personally, I think it depends on the price. I got mine for $15, so it was a bargain for me - especially compared to the price I paid for Warlords.

I think the most major thing in BTS is that spies are actually useful now. A whole new element, espionage, has been added.

I agree with Jerrymander that the new espionage system is probably the biggest overall change to the game and adds a great deal to game play. Not only are Spies more useful as he said, they're also available much, much earlier--with Alphabet rather than Communism. (!)

Besides that, the new random events are a lot of fun (though you can turn them off if you don't think so). There are some new wonders, the most significant is the Apostolic Palace. And corporations also add an interesting twist to the game--though you can choose to largely ignore them if you want to. And of course, they added a whole whack of new leaders with their own UUs and UBs.

For more detail, check the BtS info center (http://www.civfanatics.com/civ4/bts/). If and when you get BtS, be sure to install the latest patch. I also recommend playing with Bhruic's latest unofficial patches (http://forums.civfanatics.com/showthread.php?t=246057) as well.